Jennifer Otani, Ross Weiss, David Giffen, Serge Trudel, Erl Svendsen, Owen Olfert and Meghan Vankosky
Week 14 and it’s again filled with in-field monitoring, data collection, and field tour events for all our Staff! Please bookmark the Blog or subscribe to receive the latest growing season information!
Ross Weiss, David Giffen, Owen Olfert and Meghan Vankosky
Prairie temperatures continue to be cooler than average. Temperatures this week were approximately 1 °C cooler than last week (Fig. 1). The warmest temperatures were observed across MB while temperatures were cooler in western SK and across AB.
Across the prairies, 30-day average temperatures have been approximately 1.5 °C cooler than normal (Fig. 2). Average 30-day temperatures were warmest across southern MB and SK. Cooler temperatures were reported across eastern and northern AB.
Growing season temperatures (April 1-July 1, 2019) have been 1 °C cooler than average; the warmest temperatures were observed across the southern prairies (Fig. 3).
This past week, significant rainfall amounts were reported central AB (Fig. 4). Minimal rainfall was reported across MB and southern AB. Across the prairies, rainfall amounts for the past 30 days have been highly variable (Fig. 5). Dry conditions persisted across much of MB and southern AB. Rainfall was well above average in SK. Growing season rainfall amounts have been below average for most of the prairies, particularly across southern regions of AB and eastern MB (Fig. 6).
Based on modeled soil moisture (Fig. 7), recent rains have improved soil moisture values across a large area of SK. Predicted soil moisture continues to be low across large regions of eastern MB and southern AB.
The growing degree day map (GDD) (Base 5 ºC, April 1-July 7, 2019) is below (Fig. 8):
The growing degree day map (GDD) (Base 10 ºC, April 1-July 7, 2019) is below (Fig. 9):
The lowest temperatures (°C) observed the past seven days ranged from at least 13 to at least 1 °C in the map below (Fig. 10).
The highest temperatures (°C) observed the past seven days ranged from less than 15 to at least 30 °C in the map below (Fig. 11).
The maps above are all produced by Agriculture and Agri-Food Canada. Growers can bookmark the AAFC Drought Watch Maps for the growing season.
Bertha armyworm (Lepidoptera: Mamestra configurata) – Early instar bertha armyworm are predicted to begin appearing across the prairies. A model run for Saskatoon SK indicates that the hatch should be complete (Fig.1) and that BAW should be in the early instar (Fig. 2).
Important – Watch your provincial monitoring networks who are weekly recording cumulative pheromone-baited traps in Alberta, Saskatchewan, and Manitoba (pg 8).
Refer to the PPMN Bertha armyworm monitoring protocol for help when performing in-field scouting. Use the images below (Fig. 3) to help identify egg masses and the economically important larvae in canola.
Now is the time to do in-field scouting for this insect pest. Review the Insect of the Week which features bertha armyworm and its doppelganger, the clover cutworm!
Ross Weiss, David Giffen, Owen Olfert and Meghan Vankosky
Grasshopper Simulation Model Output – The grasshopper simulation model will be used to monitor grasshopper development across the prairies. Weekly temperature data collected across the prairies is incorporated into the simulation model which calculates estimates of grasshopper development stages based on biological parameters for Melanoplus sanguinipes (Migratory grasshopper).
Cool temperatures continue to result in reduced grasshopper development rates. Populations are developing into third and fourth instars. Based on model runs, approximately 13% of the population is in the first instar, 23% is predicted to be in the second instar, and 32% is in the third instar, 21% are predicted to be in the fourth instar and l4% may be in the fifth instar. Grasshopper development this season has been similar to long term average development. The following map (Fig. 1) indicates that grasshopper populations across the southern prairie are mostly in the third instar. Compared to last week development has increased across southern regions of the prairies. Grasshopper development has been greatest near Winnipeg MB.
Ross Weiss, David Giffen, Owen Olfert and Meghan Vankosky
Wheat Midge (Sitodiplosis mosellana) – Where wheat midge are present, cool, dry conditions have resulted in delayed emergence of adults. Wheat midge larvae have moved to the soil surface and pupae are appearing. In some locations adults should be beginning to emerge. The wheat midge model predicts that 45% (54% last week) of the population are in the larval cocoon stage and 47% (42% last week) of the population is predicted to have moved to the soil surface. This week 7% (3.4% last week) is predicted to be in the pupal stage. Adults have begun to emerge in localized areas in southern AB and MB.
The first map indicates the percent of the population that is in the larval stage, at the soil surface. Midge development in SK was reduced due to dry soil moisture conditions. The second map indicates that pupae may be present in some fields in southern AB and MB. It should be noted that, based on fall surveys in 2018, wheat midge populations were expected to be low across most of AB and SK.
Monitoring: When monitoring wheat fields, pay attention to the synchrony between flying midge and anthesis.
In-field monitoring for wheat midge should be carried out in the evening (preferably after 8:30 pm or later) when the female midges are most active. On warm (at least 15ºC), calm evenings, the midge can be observed in the field, laying their eggs on the wheat heads (photographed by AAFC-Beav-S. Dufton & A. Jorgensen below). Midge populations can be estimated by counting the number of adults present on 4 or 5 wheat heads. Inspect the field daily in at least 3 or 4 locations during the evening.
REMEMBER that in-field counts of wheat midge per head remain the basis of economic threshold decision. Also remember that the parasitoid, Macroglenes penetrans (photographed by AAFC-Beav-S. Dufton below), is actively searching for wheat midge at the same time. Preserve this parasitoid whenever possible and remember your insecticide control options for wheat midge also kill these beneficial insects which help reduce midge populations.
Economic Thresholds for Wheat Midge: a) To maintain optimum grade: 1 adult midge per 8 to 10 wheat heads during the susceptible stage. b) For yield only: 1 adult midge per 4 to 5 heads. At this level of infestation, wheat yields will be reduced by approximately 15% if the midge is not controlled.
Inspect the developing kernels for the presence of larvae and the larval damage.
Wheat midge and its doppelganger, the lauxanid fly, were featured as the Insect of the Week (for Wk10). Check that post for help with in-field scouting for this economic pest of wheat! The differences between midges and parasitoid wasps are featured as the current Insect of the Week (for Wk11). Not all flying insects are mosquitoes nor are they pests – many are important parasitoid wasps that actually regulate insect pest species in our field crops.
More information about Wheat midge can be found by accessing the pages from the new “Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and Field Guide”. View ONLY the Wheat midge pages but remember the guide is available as a free downloadable document as both an English-enhanced or French-enhanced version.
Diamondback moth (Plutellidae: Plutella xylostella) – Once the diamondback moth is present in the area, it is important to monitor individual canola fields for larvae. Warm growing conditions can quickly translate into multiple generations in a very short period!
Remove the plants in an area measuring 0.1 m² (about 12″ square), beat them on to a clean surface and count the number of larvae (Fig. 1) dislodged from the plant. Repeat this procedure at least in five locations in the field to get an accurate count.
Economic threshold for diamondback moth in canola at the advanced pod stage is 20 to 30 larvae/ 0.1 m² (approximately 2-3 larvae per plant). Economic thresholds for canola or mustard in the early flowering stage are not available. However, insecticide applications are likely required at larval densities of 10 to 15 larvae/ 0.1 m² (approximately 1-2 larvae per plant).
Provincial entomologists provide insect pest updates throughout the growing season so we link to their most recent information:
• Manitoba‘s Crop Pest Updates for 2019 are posted here. Access Issue #8 posted July 10, 2019 which includes more thistle caterpillar information, updated bertha armyworm pheromone trap information, the presence of low numbers of green cloverworm in some pulse crop fields, grasshopper presence, andsome higher numbers of diamondback moth larvae in some canola.
The Canadian Wildlife Health Cooperative compiles and posts information related to their disease surveillance for West Nile Virus in birds. Take note of the provincial distribution of positive WNV birds in 2018 (table posted below as reference).
The following is offered to predict when Culex tarsalis will begin to fly (Fig. 2) across the Canadian prairies. Protect yourself by wearing DEET! The regions most advanced in degree-day accumulations for Culex tarsalis, the vector for West Nile Virus, are shown in the map below. Areas highlighted lime green in the map below (Fig. 2) are on the verge of approaching sufficient heat accumulation for mosquitoes to emerge soon.
Once the adults emerge, the following map demonstrates how quickly a Culex tarsalis mosquito carrying WNV can become fully infective (i.e., when it has accumulated 109 base 14.3° degree days) – as quickly as 20-22 days, given the current environmental conditions in the highlighted areas of the map below (Figure 3).
Public summer field events – Coming to a field near you – Prairie field crop entomologists are already scheduled to be at these 2019 field tour events from May-August (be sure to re-confirm dates and details as events are finalized):
• July 22, 2019: Pulse grower gathering held near Three Hills AB. Check Alberta Pulse Growers Event Page for more information. Entomologists presenting: Graduate students from Dr. Maya Evenden’s (U of A) working on pea leaf weevil.
• July 23-24, 2019: Crop Diagnostic School, Scott Saskatchewan. Read more about this event. Entomologists presenting: Meghan Vankosky, Tyler Wist.
• July 24, 2019: Crops-a-Palooza. Held at Canada-Manitoba Crop Diversification Centre (CMCDC), Carberry, Manitoba. Read more about this event. Entomologist participating: John Gavloski, Vincent Hervet, Tharshi Nagalingam, Bryan Cassone.
• August 8, 2019: 2019 Wheatstalk to be held at Teepee Creek AB. View event info/registration details. Entomologists tentatively participating: Jennifer Otani, Shelby Dufton, Amanda Jorgensen, Boyd Mori.
• August 8, 2019. Horticulture School. Agriculture and Agri-Food Canada Research Farm, Portage la Prairie, Manitoba. View event info/registration details. Entomologist presenting: John Gavloski, Kyle Bobiwash.
The case of the prairie grasshoppers: There are 80 grasshopper species on the prairies but only a few that are considered pests. These include Packard (Melanopus packardii), clearwinged (Camnula pellucida), migatory (Melanopus sanguinipes), two-striped (Melanopus bivittatus) and Bruner Melanoplus bruneri) grasshoppers. They are recognizable as grasshoppers (similar body shape and distinctive large rear legs) and, depending on the species, range in size from 21 to 40 centimetres (8.25 to 15.75 inches). Most of these pest species can be distinguished by colouring and size. However, the Bruner and migratory grasshoppers are difficult to tell apart, needing to rely on examining the male genitalia (see Insect of the Week post from July , 2018).
The case of the innocuous versus the evil twin: When making pest management decisions, be sure that the suspect is actually a pest. This can be challenge since insects often mimic each other or look very similar. An insect that looks, moves and acts like a pest may in fact be a look-alike or doppelganger.
Doppelgangers may be related (e.g. same genus) or may not be related, as in the case of monarch butterflies (Danaus plexippus) and viceroys (Limenitis achrippus). Doppelgangers are usually relatively harmless but sometimes the doppelganger is a pest yet their behaviour, lifecycle or hosts may be different.
Correctly identifying a pest enables selection of the most accurate scouting or monitoring protocol. Identification and monitoring enables the application of economic thresholds. It also enables a producer to select and apply the most effective control option(s) including method and timing of application. For the rest of the growing season, the Insect of the Week will feature insect crop pests and their doppelgangers.